When measuring distance in miles (or kilometers) Google Earth shows two decimal points . This is not a 3rd grade standard, but I like to explain rounding to the closest mile to students because it ties in directly to rounding to the closest hundred. I explain that the two digits following the decimal point (tenths and hundredths place) are the same as as a fraction with those two numbers in the numerator and 100 in the denominator. I very quickly review how to round the the closest hundred, between zero and one hundred. They should be very familiar with this at this point in the year.

Here is a YouTube tutorial on how to measure distances in Google Earth.

The number of countries students can search is limited, at least initially. I have found that both Iceland and Indonesia have recently active, visible volcanoes. Prior to sending students off on a more open-ended search, it's important to note that not all regions have high quality images before you let students search anywhere they want. I've learned this the hard way, so let me save you the trouble!

Here are directions for the student activity that can be projected for easy review:

3. Cut and paste the volcano name and country into the Google Earth search box.

4. Find a nearby town or city.

5. Set the ruler tool to miles.

6. Set the ruler tool to miles. Measure the distance between the volcano (any location on the volcano is fine) and the town.

7. Record the data.

If you would like to provide more guidance for students in using Google Earth, this document (5 Indonesian Volcanoes) contains verified place names and latitutde and longitude markers that can be cut and pasted directly into the Google Earth search box. Here is how the list I've provided can used to search by name and here is an explanation of how it can be used to search by latitude and longitude.

Language Goal: Students will state, "I estimate that (name of volcano) is ____ miles from (the closest town/name of town). My measurement showed that (name of volcano) is _____ miles from (town). The actual distance is about ________ miles greater than/less than my estimate."

This will take some practice, as the volcanoes have tricky names. Don't let them get hung up on the pronunciation of proper nouns, especially something as obscure as volcano names in foreign countries!

Big Idea:
In order to approximate a total, or to help check the reasonableness of an answer, students need to be able to round to the nearest 10 or 100. Check out this lesson for a fun game that gives them practice rounding, adding, and subtracting.